EP3300818B1 - Method for sintering a dental structure and arrangement for sintering a dental structure - Google Patents

Description

The present invention relates to a method for sintering a dental construction. In addition, the invention relates to an arrangement for sintering a dental construction with a sintering furnace, in which a closable heating chamber is formed and at least one dental construction arranged in the heating chamber during sintering.

Sintering has been used as an essential manufacturing step in the manufacture of dental prosthetic items for many decades. It serves above all to ensure that the components of the dental prosthetic item become so hard that the dental prosthetic items manufactured in this way withstand the high stresses to which a human dentition is exposed.

In the dental industry, dental technicians have been using sintering furnaces for many years, which are specially designed for sintering dental constructions. An example of this is given in the EP 2 703 760 B1 out. This shows in particular a vacuum container arranged in the boiler room, in which the dentures are arranged during sintering. Also the EP 2 974 689 A1 shows an arrangement for sintering a dental workpiece in a housing in which a vacuum can be generated. The dental workpiece is suspended from a holding device.

If dental constructions with a metal component are used in the sintering furnaces mentioned during sintering, the reaction with oxygen present in the boiler room can lead to oxidation. This has a negative impact on the surface quality of the manufactured dental construction. In addition, the production is delayed because an additional step for cleaning the oxidized surface is necessary.

The EP 2 792 332 B1 shows an arrangement with at least one workpiece to be sintered and with at least one support material. The workpiece protrudes from the support material. In addition, a protective gas is supplied to the workpiece through the support material. The support material can be an oxygen-binding material, the support material having a higher affinity for oxygen than the workpiece. Oxygen affinity is understood to mean the endeavor of a substance or a material to bind oxygen to itself, in particular through a chemical reaction. This support material can be commercially available so-called sintered beads, e.g. B. from yttrium partially stabilized zirconia. Other ceramic support grains or mixtures thereof can also be used as the support material. An additional material can also be added to the ceramic support grains. A material or a material mixture which has at least one chemical element or at least one chemical compound which has a higher affinity for oxygen than the material of the workpiece or as the material of the ceramic support grains is used as the additional material. Such additional materials with high affinity for oxygen are e.g. B. metals or metal alloys. Ceramic additional materials can also be used. The additive can be in pellet or powder form. The additional material may be e.g. B. cobalt, chromium, molybdenum, titanium or titanium alloys.

A disadvantage of the last-mentioned document is the high manufacturing outlay, since a protective gas in the form of argon and / or nitrogen must always be added. This means that the dental technician must always have a protective gas available for refilling. In addition, the constant use of protective gas is relatively expensive.

The invention further relates to a method in which the method for sintering a dental construction is additionally carried out using an oxygen-affine oxygen binding element, the sintering of the dental construction taking place at least temporarily in an air atmosphere, wherein the oxygen binding element consists essentially of titanium-containing metal or a titanium-containing metal alloy, wherein the proportion of titanium in the oxygen binding element is at least 80% and wherein the dental construction consists of a cobalt-chromium-molybdenum alloy.

The US 5,911,102 shows such a dental construction, which can also have cobalt, chromium and molybdenum, the dental construction consisting of a maximum of 60 percent by weight of chromium, cobalt and molybdenum. The remaining component or the main component is titanium. The oxygen binding element ("getter") can consist of titanium or a titanium alloy. The disadvantage here is that the titanium of the dental construction also largely binds the oxygen and the surface of the dental construction can thus be negatively influenced by oxidation.

The object of the present invention is therefore to create an improved method and an improved arrangement compared to the prior art. In particular, the method and the arrangement should be less complex and negative influences on the surface of the dental construction during sintering should be prevented.

This is achieved by a method with the features of claim 1. The object of the invention is also achieved by an arrangement with the features of claim 10.

An air atmosphere can preferably be defined such that it has an oxygen volume fraction in a range from 20% to 22% and a nitrogen volume fraction in a range from 77% to 79%. On the one hand, the oxygen binding element in the air atmosphere is bound by the oxygen binding element, as a result of which the oxygen does not or hardly oxidizes on the surface of the dental construction. On the other hand, no complex shielding gas supply is necessary, but it becomes the normal one Ambient air is used as the atmosphere during sintering. The sintering is therefore free of inert gas.

It is preferably provided that the sintering of the dental construction begins in an air atmosphere. Particularly preferably, there is no active influence on the air atmosphere during the entire sintering process. Changes in the composition of the air atmosphere therefore only result from the sintering process itself and from the oxygen binding element.

It is generally possible for an air atmosphere to be used for sintering which deviates from the air composition occurring on the earth's surface. Depending on the application, additional gas components can therefore be fed into the boiler room. However, it is preferably provided that the air atmosphere has an oxygen volume fraction of exactly 20.94% and a nitrogen volume fraction of exactly 78.08%. It is further provided that the air atmosphere has an argon volume fraction of 0.8 to 1%, preferably 0.93%. In addition, the air atmosphere has a volume fraction of trace gases (including carbon dioxide, neon, helium, methane, krypton, hydrogen, etc.) of less than 0.1%, preferably 0.04%. This air composition corresponds to dry air at sea level at 1,013.25 hPa. If the measurement of the air composition is carried out with humid air and at different sea level and other air pressure conditions, the volume proportions may differ slightly from the values given above.

During the entire sintering process, the percentage distribution of the air atmosphere changes in such a way that the oxygen content decreases because the oxygen molecules are bound to the oxygen binding element. This means that the air atmosphere in the boiler room is especially present at the start of sintering. However, it is also provided that in a heating phase when the sintering temperature has reached at least 80%, preferably at least 90%, the air atmosphere continues to have an oxygen volume fraction in a range of Has 20% to 22% and a nitrogen volume fraction in a range from 77% to 79%. It is assumed that these gases (oxygen and nitrogen) have the same coefficient of thermal expansion. The sintering temperature can be, for example, in a range between 1,100 ° C and 1,500 ° C, preferably between 1,200 ° C and 1,250 ° C. With a sintering process totaling, for example, 5 to 10 hours, preferably 8 to 9 hours, the sintering temperature is reached after about 1 to 3 hours. The sintering temperature is held for 3 to 6 hours, preferably for 4.5 to 5.5 hours. This is followed by a cooling phase. Of course - especially with regard to the temperature profile - sintering processes that differ considerably can be carried out depending on the type and composition of the dental construction to be sintered.

In principle, it is preferably provided that the sintering is carried out in a lockable heating chamber of a sintering furnace. Special sintering furnaces for sintering dental constructions have been used by dental technicians for many years.

In principle, it should not be excluded that there is at least occasional overpressure during sintering. According to a first variant, however, it can be provided that the sintering pressure in the boiler room is less than 1,030 hPa. Normal pressure prevails in the boiler room during sintering. This normal pressure of 1,013.25 hPa at sea level predominates at the beginning of the sintering process. During heating and sintering, the air pressure in the boiler room can fluctuate within certain limits without deliberate interference.

According to a second variant, it can be provided that a negative pressure of more than 300 hPa or a vacuum, preferably a rough vacuum between 300 and 1 hPa or a fine vacuum between 1 and 0.001 hPa, is generated in the boiler room, the sintering being carried out under negative pressure or in a vacuum is carried out. Even finer vacuums can be created. That in The vacuum generated in the boiler room can already be present at the start of the sintering process. The vacuum can also be maintained only temporarily, that is to say for a specific period or at different periods. The vacuum or negative pressure is preferably maintained during the entire sintering process. In general, there is still air in each of the vacuums mentioned, only the concentration of the air is reduced. This means that even in a vacuum, the percentage distribution of the volume fractions of oxygen, nitrogen, argon etc. still corresponds to that of an air atmosphere. In a vacuum, only the total number of molecules in the boiler room is lower. Specifically, at normal pressure there are about 2.7x10 ¹⁹ (27 trillion) molecules in every cm ^{3 of} air. In a rough vacuum there are 10 ¹⁹ (10 trillion) to 10 ¹⁶ (10 trillion) molecules in every cm ³ , while in a fine vacuum there are still 10 ¹⁶ (10 trillion) to 10 ¹³ (10 trillion) molecules in every cm ³ ,

In order to prevent oxidation on the surface of the dental construction, it is provided that the oxygen affinity of the oxygen binding element is greater than the oxygen affinity of the dental construction.

According to the invention, it is provided that the oxygen binding element consists essentially of metal or a metal alloy. The metal content should be at least 85%, preferably at least 95%. For this purpose, it is provided according to the invention that the oxygen binding element contains titanium, the proportion of titanium in the oxygen binding element being at least 80%, preferably at least 95%. In particular, titanium with a purity of at least 98.5% is used. The titanium used has a melting temperature of approx. 1,700 ° C and a boiling temperature of approx. 3,260 ° C. Depending on the alloy composition, properties such as melting or boiling temperature also vary.

In general, the oxygen binding element can be powdery, granular, solid or in some other form. It is important that the surface of the oxygen binding element is relatively large relative to its volume. It is therefore preferably provided that the oxygen binding element is sponge-shaped.

Dental constructions can be in the form of bridges, abutments, crowns, individual constructions, bars, etc. There is no limit to the final shape.

With regard to the dental construction, it is provided according to the invention that it essentially consists of a cobalt-chromium alloy. The cobalt-chromium alloy preferably has a proportion of 50 to 70 percent by weight of cobalt and a proportion of 20 to 31 percent by weight of chromium. According to the invention, the cobalt-chromium alloy consists of at least 80 percent by weight of cobalt and chromium and very preferably at least 90 percent by weight of cobalt and chromium. In addition, the cobalt-chromium alloy can also have at least one or more proportions selected from the group consisting of molybdenum (Mo), manganese (Mn), silicon (Si), tungsten (W), iron (Fe), nickel (Ni ), Aluminum (Al), titanium (Ti), phosphorus (P), boron (B), cadmium (Cd), beryllium (Be), carbon (C), sulfur (S), oxygen (O) and nitrogen (N ). It is provided according to the invention that the cobalt-chromium alloy has a proportion of at least 3 percent by weight of molybdenum, the proportion of molybdenum preferably being between 5 and 8 percent by weight. For example, the dental construction can be machined out of a molded blank, preferably milled out, as it is in the WO 2015/154872 A1 is described. The materials listed in this document therefore form the dental construction. Standards that can be used for the composition of cobalt-chromium alloys include ISO 5832-12 or ASTM F1537.

If a titanium-based alloy were used for the dental construction, not only would the titanium-based oxygen binding element attract oxygen, but also the dental construction itself, whereby the Dental structure would oxidize during sintering. To avoid this, it is therefore particularly preferred that, on the one hand, an alloy is used for the dental construction, which consists of at least 95 percent by weight of cobalt, chromium and molybdenum, and, on the other hand, an oxygen binding element is used, which consists of at least 95 percent by weight of titanium. This combination results in a special synergy effect in that the titanium of the oxygen binding element binds a large part of the oxygen in the air atmosphere and does not or hardly oxidizes the surface of the dental construction.

The object of the invention is also achieved by an arrangement with the features of claim 10. Accordingly, the arrangement for sintering a dental construction has a sintering furnace in which a closable heating space is formed, the heating space during sintering being at least temporarily filled with an air atmosphere which preferably has an oxygen volume fraction in a range from 20% to 22% and has a nitrogen volume fraction in a range from 77% to 79%. In addition, at least one dental construction and one oxygen-binding oxygen binding element are arranged in the boiler room during sintering. When sintering in the boiler room, there is preferably an air pressure of less than 1,030 hPa, preferably normal pressure, negative pressure or a vacuum.

With regard to the boiler room, it is preferably provided that the boiler room is formed either directly in a housing of the sintering furnace or in a vacuum container projecting into the housing. The boiler room is the area that is heated and directly houses the dental construction to be sintered. Several different dental constructions can also be sintered at the same time.

According to a preferred embodiment, it is provided that the at least one oxygen binding element is stored in a container, preferably arranged in a lateral area of the boiler room.

It is preferable to ensure that the oxygen binding element is not in direct contact with the dental construction. The oxygen binding element is therefore arranged at a distance from the dental construction.

In order to avoid warping of the material to be sintered, it is preferably provided that at least one holding device arranged in the heating space is provided for holding the dental construction. It is preferably provided that the dental construction is suspended from the holding device in the boiler room. Smaller jobs in particular can also simply be parked in the boiler room.

The arrangement preferably also has a vacuum or vacuum generating device with which the vacuum or vacuum, preferably a rough vacuum or a fine vacuum, can be generated in the boiler room. In particular, a vacuum pump can be used with which a pressure of less than 1 mbar (corresponds to 1 hPa) can be generated in the boiler room.

Fig. 1

in einem Querschnitt einen Sinterofen mit in einem Vakuumbehälter angeordneter Dentalkonstruktion,

Fig. 2

in einem Querschnitt einen Sinterofen mit direkt im Heizraum angeordneter Dentalkonstruktion und

Fig. 3a-3c

verschieden Ansichten einer Haltevorrichtung samt daran aufgehängten Dentalkonstruktionen.

Further details and advantages of the present invention are explained in more detail below with reference to the description of the figures and with reference to the exemplary embodiments illustrated in the drawings. In it show:

Fig. 1

in a cross section a sintering furnace with a dental construction arranged in a vacuum container,

Fig. 2

in a cross section a sintering furnace with a dental construction arranged directly in the boiler room and

3a-3c

different views of a holding device including dental constructions suspended from it.

Fig. 1 shows a sintering furnace 3 in a cross section. This sintering furnace 3 has a furnace space R which can be closed by the door 7 and a housing 8. A preferably tubular vacuum container 9 projects into the furnace chamber R. By heating the furnace chamber R, the one formed in the vacuum container 9 is also formed Boiler room H heated. The vacuum container 9 is connected to the door 7 of the sintering furnace 3. By means of a vacuum or vacuum generating device 6, which is only shown schematically, a vacuum or a vacuum can be generated in the vacuum container 9. An air atmosphere L is present in the vacuum container 9. Two dental constructions 1 are suspended from a holding device 5 arranged in the vacuum container 9. In the containers 4 arranged laterally next to the dental constructions 1 there are oxygen-affine oxygen binding elements 2. If the sintering takes place with the dental construction 1 arranged in the vacuum container 9, that area of the vacuum container 9 which protrudes from the furnace space R can be separated from the inside with a separating device 10 shown in broken lines so that not too much heat is lost in the left-sided, unused space. As an alternative to the variant shown, it can also be provided that the vacuum container 9 remains in the furnace chamber R and only one closure device of the vacuum container 9 has to be opened in order to insert and remove the dental construction 1.

In contrast, according to Fig. 2 the dental constructions 1 are arranged directly in the furnace space R filled with an air atmosphere L, which at the same time forms the heating space H. The furnace space R or the heating space H is heated by means of a heating device (not shown in more detail).

The Fig. 3a shows the holding device 5 together with the suspended dental structures 1 in a longitudinal section, the Fig. 3b in a cross section and the Fig. 3c in a perspective view. The containers 4 are held on the side supports 12 of the holding device 5 via guides 11 designed as recesses. The oxygen binding elements 2 placed in the container 4 are not shown here. A base plate 13 with a trough-shaped depression is arranged between the two side supports 12. In the upper area, the side supports 12 are connected via a holding bracket 14. In the recesses 15 of this holding bracket 14 16 suspension elements 17 are held by pins. On this The dental constructions 1 are in turn held on suspension elements 17. The dental construction 1 shown on the right-hand side is designed as a circular bridge construction, while the dental construction 1 shown on the left-hand side is designed as a smaller bridge element through which five teeth (see Fig. 3b ) are reproduced.

LIST OF REFERENCE NUMBERS

1

Dental design

2

Oxygen binding element

3

sintering furnace

4

container

5

holder

6

Vacuum or vacuum generating device

7

door

8th

casing

9

vacuum vessel

10

separating device

11

guides

12

side straps

13

baseplate

14

retaining bracket

15

deepening

16

pencils

17

suspension elements

L

air atmosphere

H

boiler room

Claims (13)

1. A method for sintering a dental construction (1) using an oxygen-affine oxygen binding element (2), wherein the sintering of the dental construction is carried out at least at times in an air atmosphere (L), wherein the oxygen binding element (2) substantially consists of a metal containing titanium or of a metal alloy containing titanium, wherein the proportion of titanium in the oxygen binding element (2) is at least 80 percent by weight, wherein the dental construction (1) consists of an alloy which contains cobalt, chromium and molybdenum, characterized in that the alloy consists of at least 80 percent by weight of cobalt and chromium and that the alloy comprises a proportion of at least 3 percent by weight of molybdenum.
2. The method according to claim 1, wherein the air atmosphere (L) comprises a volume proportion of oxygen in a range from 20 % to 22 % and a volume proportion of nitrogen in a range from 77 % to 79 %.
3. The method according to claim 1 or 2, wherein the sintering of the dental construction (1) in the air atmosphere begins with an air pressure of at least 1.030 hPa.
4. The method according to at least one of the claims 1 to 3, wherein in a heating phase when reaching at least 80 %, preferably at least 90 %, of the sintering temperature, the air atmosphere still comprises a volume proportion of oxygen in a range from 20 % to 22 %, a volume proportion of nitrogen in a range from 77 % to 79 % and an air pressure of at least 1.030 hPa.
5. The method according to at least one of the claims 1 to 4, wherein the sintering is carried out in a closable heating room (H) of a sintering furnace (3).
6. The method according to claim 5, wherein in the heating room (H) during the sintering there is either standard pressure or a low pressure of more than 300 hPa or a vacuum, preferably of a medium vacuum between 300 and 1 hPa or a high vacuum between 1 and 0.001 hPa, is generated, wherein the sintering is carried out under low pressure or in a vacuum.
7. The method according to at least one of the claims 1 to 6, wherein the proportion of titanium in the oxygen binding element (2) is at least 95 %.
8. The method according to at least one of the claims 1 to 7, wherein the cobalt-chromium-alloy comprises cobalt in a proportion of 54 to 70 percent by weight and chromium in a proportion of 20 to 31 percent by weight.
9. The method according to at least one of the claims 1 to 8, wherein the cobalt-chromium-alloy consists of cobalt and chromium by at least 90 percent by weight.
10. An arrangement for sintering a dental construction (1), in particular for carrying out a method according to at least one of the claims 1 to 9, comprising

    - a sintering furnace (3) in which a closable heating room (H) is formed, wherein the heating room (H) during sintering is at least temporarily filled with an air atmosphere (L),

    - at least one dental construction (1) arranged in the heating room (H) during sintering, wherein the dental construction (1) consists of an alloy which contains cobalt, chromium and molybdenum, wherein the alloy consists of at least 80 percent by weight of cobalt and chromium and wherein the alloy comprises a proportion of at least 3 percent by weight of molybdenum, and

    - at least one oxygen-affine oxygen binding element (2) arranged in the heating room (H) during sintering, wherein the oxygen binding element (2) substantially consists of a metal containing titanium or of a metal alloy containing titanium, wherein the proportion of titanium in the oxygen binding element (2) is at least 80 percent by weight.
11. The arrangement according to claim 10, wherein the at least one oxygen binding element (2) is stored in a container (4), preferably arranged in a lateral area of the heating room (H).
12. The arrangement according to claim 10 or 11, comprising at least one holding device (5) for holding the dental construction (1), the holding device (5) being arranged in the heating room (H).
13. The arrangement according to at least one of the claims 10 to 12, comprising a device (6) for generating a low pressure or a vacuum, wherein with this device (6) the low pressure or the vacuum, preferably a medium vacuum or a high vacuum, can be generated in the heating room (H).

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